New Species of Extinct River Dolphin Sheds Light on Evolution of Freshwater Cetaceans

A certain extinct dolphin may actually tell researchers a bit more about unusual river dolphins. Scientists have found a new fossil dolphin species that may shed some light on the relationships between these freshwater dolphins.

River dolphins are a somewhat strange group of cetaceans. Unlike other whales and dolphins, they live in freshwater streams and estuaries. Because of life in these muddy waters, some of these dolphins are functionally blind and have very small dorsal fins. Yet despite similar appearances, South Asian river dolphins of the Ganges and Indus rivers are only very distantly related to other river dolphins of the Amazon and Yangtze rivers.

This newly discovered dolphin, though, may shed some light on the relationships between these dolphins. The new species is called Huaridelphis raimondii, and is the smallest species of its family yet known. It likely lived during the Miocene within the Pisco Basin, which today is a desert on the coast of Peru. It belonged to a rare extinct family of marine dolphins, the squalodelphinids, which are related to the Ganges and Indus river dolphins living today. In fact, it's possible that the river dolphins are all descendants of ocean-dwelling species, like Huaridelphis raimondii.

Currently, researchers hope to unearth more fossils in order to make more connections between these fossils and present day species. This, in turn, could tell scientists a bit more about the evolutionary history of river dolphins.

"For the past 30 years, many fossil cetacean species were described based on material from the Pisco Basin, dated from the Eocene to the Pliocene," said Olivier Lambert, lead author of the new study, in a news release. "And we are still far from the end of the study for this hot spot of marine mammal paleontology."

The findings are published in the Journal of Vertebrate Paleontology.